Project Summary Accurate and sensitive measurement of cognitive change is required to advance the understanding of normative cognitive aging and improve the detection of the subtle cognitive changes during preclinical stages of neurodegenerative diseases, such as Alzheimer's. In response to RFA-AG-18-012, we propose to develop infrastructure for the Mobile Monitoring of Cognitive Change (M2C2) that will provide the research community with open, flexible, and usable tools to enable scientific progress that depends on the sensitive and accurate measurement of cognitive change. We will build this infrastructure by accomplishing the following aims. First, we will establish rapid iterative piloting and test development procedures that accelerate our capacity to prototype, deploy, evaluate, and optimize candidate mobile cognitive tests to meet psychometric, accessibility, and engagement benchmarks (Aim 1: Iterative Design & Piloting). Second, evaluate reliability, construct validity, and longitudinal validity of mobile cognitive testing procedures (Aim 2: Reliability & Validity) in a racially diverse probability sample. Third, we replicate psychometric results in an independent, nationally representative probability based sample, and create nationally representative norms (Aim 3: Replication). And fourth, we will test our pipeline and procedures for incorporating new measures into the mobile assessment infrastructure by evaluating novel measures for inclusion that are nominated by investigators outside of our immediate research team (Aim 4: Extension).